1. Field
The present invention relates to a manufacturing method and an apparatus for a fiber reinforced polymer (FRP) bar, and more particularly, to a manufacturing method and an apparatus for a FRP bar which does not cause excessive bending deflection even though a fiber having a low elastic modulus is used, by introducing a compression force in advance. In addition, the present invention relates to a method and an apparatus for manufacturing a hybrid FRP bar by using at least two kinds of fibers so that the fibers may be easily distributed to specific locations at the section of the manufactured hybrid FRP bar, and a nozzle for such an apparatus.
2. Description of the Related Art
A steel bar used for a reinforced concrete structure is always exposed to possibility of corrosion. A steel bar in concrete is highly likely to contact moisture due to cracks or the like, and in particular, the steel bar is corroded due to residual moisture in the concrete, in addition to cracks. When the steel bar is corroded, the volume of the steel bar expands, which results in separation of concrete cover. Therefore, the reinforced concrete structure loses integrity, which is an essential requirement of the reinforced concrete structure, and is not able to serve as a structural member.
In order to solve this problem, rod-shaped products manufactured using a fiber reinforced polymer (FRP) have been used instead of steel bars distributed in a concrete structure or to assist the steel bars. Such a rod-shaped product manufactured using FRP is generally called “FRP bar” or “FRP re-bar” since it is used for reinforcing a concrete structure.
Korean Patent Registration No. 10-0702629 and Korean Unexamined Patent Publication No. 10-1987-3861 disclose a technique for manufacturing such a FRP bar. In the prior art, a FRP bar is manufactured by a manufacturing apparatus including a fiber winding reel, a resin supplier, a nozzle, a heater and a drawer. In order to manufacture the FRP bar, first, fibers as thin as threads, supplied from the fiber winding reel, are bound into a bundle and drawn to the drawer. In this time, while passing through the resin supplier, the fibers are formed into a rod shape while entering the nozzle together with a resin, and the resin is hardened through the heater, thereby making the FRP bar.
The fibers used for manufacturing a rod-shaped FRP bar having a circular, oval or polygonal section by bundling the fibers impregnated in a resin as described above use carbon fibers, aramid fibers, steel wires, glass fibers or the like, among which glass fibers are advantageous for cost reduction. However, when the FRP bar is manufactured using glass fibers, the glass fibers have a lower elastic modulus than the steel bar even though its tensile strength is much greater than that of the steel bar. Therefore, if the FRP bar is used for reinforcing a bending member, a great drooping is caused at the bending member. In other words, if the FRP bar is manufactured using a fiber having a low elastic modulus such as a glass fiber, an excessive bending deflection is caused at a concrete structure to which a bending load is applied.
As a solution, there has been proposed a technique for manufacturing a FRP bar by mixing several kinds of fibers having different elastic modulus. The FRP bar manufactured using several kinds of fibers together may be called a “hybrid FRP bar”. The hybrid FRP bar may ensure good economical feasibility since several kinds of fibers are mixed, thereby ensuring more improved elastic modulus in comparison to a FRP using only glass fibers. The hybrid FRP bar may use, for example, a glass fiber having a low elastic modulus and a carbon fiber having a high elastic modulus.
When manufacturing a hybrid FRP bar by using several kinds of fibers, it may be needed to distribute the several kinds of fibers at different locations in the section of the FRP bar. If the hybrid FRP bar uses a glass fiber and a carbon fiber as in the above example, it may be needed to locate the glass fiber at the center of the section and the carbon fiber at the periphery of the section.
The fibers used for manufacturing a FRP bar have a very small diameter like threads, and several ten or hundred fibers are bound for use. If there is proposed a technique capable of effectively manufacturing a hybrid FRP bar in a state where several kinds of such fibers are used and also each kind of fiber is distributed at a specific location on the section of the FRP bar as designed, the hybrid FRP bar will be efficiently used suitable for a stress situation or other use conditions.